Streptococcus pneumoniae are pathogens that cause various diseases including respiratory tract infections such as pneumonia and bronchitis, sinusitis, otitis media, and meningitis. Among the diseases caused by the infection with the Streptococcus pneumoniae, pneumonia is a disease with a high death rate in elderly people aged 65 or older, following cancer, heart disease and cerebral stroke, and is a big issue. In addition, since Streptococcus pneumoniae that have become resistant to antibiotics such as penicillin are increasing, the number of cases where the treatment of the disorder due to the infection with the Streptococcus pneumoniae is difficult has been increased. Especially, penicillin-resistant strains have increased from late 1980s around the world, and it is said that if low susceptible strains are included, currently the penicillin-resistant strains occupy approximately half of clinical isolates.
Currently, in order to treat pneumococcal infection, surgical treatments and antimicrobial agents are used in combination in the case of patients with otitis media or sinusitis. For the treatment of patients with severe infection such as pneumonia, meningitis, and postoperative wound infection, it is essential to administer antimicrobial agents which are expected to be effective against certain pathogens. Typically, carbapenem antibiotics or penicillin antibiotics that serve as the antimicrobial agent are administered in high doses, but in severe cases, carbapenem antibiotics and glycopeptide antibiotics are used in combination.
Thus, although there is a concern that the use of carbapenem antibiotics or glycopeptide antibiotics may increase resistant bacteria, carbapenem antibiotics and glycopeptide antibiotics are still used because they are useful as a therapeutic agent for penicillin-resistant pneumococcal infection.
The number of bacteria resistant to antibiotics has increased on the front lines of health care. Under such circumstances, there is a need for novel antibiotics that have antimicrobial activity against penicillin-resistant bacteria and that can be clearly distinguished structurally. For example, it is known that 3,4′-dideoxymycaminosyltylonolide has an excellent antimicrobial effect against general Gram-positive bacteria and Gram-negative bacteria (See Non-Patent Literatures 1 and 2, Patent Literature 1). However, antimicrobial activity against penicillin-resistant Streptococcus pneumoniae (hereinafter, may be briefly referred to as “PRSP”) is not described in the above-mentioned Literatures. Since generally, macrolide antibiotics can be used reliably in medical care, it is desirable to search for novel anti-PRSP agents from macrolide antibiotics and thus to obtain novel anti-PRSP agents.    Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 02-275894    Non-Patent Literature 1: The Journal of Antibiotics, Vol. 45, No. 1, pp. 144-146, 1992    Non-Patent Literature 2: Antimicrobial Agents and Chemotherapy, Vol. 36, No. 8, pp. 1699-1702, 1992